Pressure sensitive adhesives have for a long time been used for attaching medical devices, such as ostomy appliances, dressings (including wound dressings), wound drainage bandages, devices for collecting urine, orthoses and prostheses to the skin.
Hydrocolloid adhesives containing hydrophilic particles or absorbents, which absorb moisture into the adhesive bulk and transmit moisture when conditions are saturated, are one well-known group of pressure sensitive adhesives useful for attaching medical devices to the skin. However, the retention of moisture in hydrocolloid adhesives may cause changes in the adhesive, such as swelling, loss of cohesion and disintegration. Non-absorbing adhesives on the other hand, may trap excessive moisture between the skin and adhesive, causing weakening of adhesion and maceration of the skin.
An alternative to the absorbing adhesives described above is a liquid impermeable, moisture permeable adhesive such as polyurethane, silicone and polyacrylate.
A liquid impermeable, moisture permeable adhesive does not absorb the moisture but rather permeates the water away from the skin surface. Thus, the swelling effect caused by the hydrocolloids will usually not occur.
U.S. Pat. No. 4,477,325 describes a skin barrier composition made of EVA, PIB and water absorbing particles or polymers. The EVA may contain from 25 to 65% by weight of vinyl acetate.
International Patent Application No. WO 2009/006901 describes pressure sensitive adhesives based on polar ethylene copolymers and a polar oil or a combination of polar oils with an excellent skin adhesion. These adhesives are very soft and have a very high moisture vapour transmission rate, which makes them breathable and very skin friendly.
Optimal adhesives for an ostomy base plate have to perform under a variety of conditions, such as differences in fluidity and amount of stoma exudates, body shape, skin firmness, skin irregularities, activity and perspiration level and of course the variation in the end-users preferred changing pattern of the device. In order to oblige to all these demands, it can sometimes be favourable and easy to add a tackifying component in order to increase the adhesive performance of the adhesive.
Resins are most often added to control the tack, i.e. reduce moduli and increase the glass transition temperature of the adhesive. Resins, however, increase the aggressiveness of the adhesives; this causes stripping of the skin upon removal and consequently makes the adhesives less skin friendly. These adhesives are therefore less suited for end-users who desire a frequent changing pattern but still are reliant on increased adhesive strength.
It has surprisingly been found that using polyisobutylene, even though apolar in nature and with a low glass transition temperature can be added to the polar adhesives described in International Patent Application No. WO 2009/006901 increasing the tack and the adhesive performance and still maintain the necessary storage stability and skin friendliness.
The use of polyisobutylene as a tackifying agent lowers the amount of cell stripping compared to utilizing resins. The addition of an apolar component will cause a decrease in the permeability of the adhesive. However, it has been found that adhesives with a sufficient moist vapour transmission rate to maintain a healthy skin of the end-user can be produced.